In the prior art, there has been a method for automatically adjusting the brightness of a single lamp according to the light intensity to realize the energy saving of the single lamp. For example, the technical solution disclosed in Patent Application CN200710053895.5 comprises sensing the light intensity by a photosensitive sensor, feeding back the light intensity to a circuit, and automatically adjusting, by the circuit, the brightness of the lamp according to the light intensity. However, for a lighting system with a large number of lights, in addition to the use of more energy-efficient lights and lamps and turning off the lights in some areas which do not need lighting, there is no more effective lighting energy saving method for the entire lighting system.